Conveying rollers pair and image forming apparatus

ABSTRACT

A conveyance rollers pair includes a first roller and a second roller. The first roller has a uniform outer diameter and rotates around an axis. The second roller conveys a medium held between the first roller and the second roller while rotating around an axis. The second roller includes a shaft part, a plurality of columnar elastic members and a plurality of tube members. The shaft part extends in an axial direction and is supported rotatably around the axis. The elastic members are fixed to an outer circumferential surface of the shaft part at intervals in the axial direction. Each of the tube member has heat-shrinking property and water-repellency, adheres closely to an outer circumferential surface of the elastic member, and has both end portions which are protruded outward from both axial ends of the elastic member and have a diameter smaller than an outer diameter of the elastic member.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese patent application No. 2022-121499 filed on Jul. 29, 2022, which is incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a conveying rollers pair which conveys a medium and an image forming apparatus.

A registration rollers pair composed of a first roller formed of a rigid body and a second roller formed of an elastic body with a low friction layer formed on the outer surface is known. The registration rollers pair is provided with a rotating member that abuts on the first roller to prevent deflection when the first roller tries to deflect in a direction away from the second roller. This prevents the occurrence of “wrinkles” on the sheet passing through the nip area and variations in the conveyance force of the sheet.

Incidentally, when the registration rollers pair continuously conveys a narrow sheet in the axial direction, a load may be concentrated in the axial center portion of the first and second rollers. Then, the low-friction layer is shifted with respect to the elastic body of the second roller in the sheet conveyance direction, and the twisted “wrinkles” are sometimes generated on the low-friction layer. When the “wrinkles” are generated on the low-friction layer, there is a possibility that the proper sheet conveyance may be hindered, for example, the “wrinkles” are generated on the sheet conveyed while being held between the registration rollers, or variations in the conveyance force of the sheet is generated. In the above-mentioned registration rollers pair, sufficient consideration is not given to suppressing the generation of the “wrinkles” on the low-friction layer of the second roller.

SUMMARY

A conveyance rollers pair according to present disclosure includes a first roller and a second roller. The first roller extends in an axial direction, has a uniform outer diameter and rotates around an axis. The second roller conveys a medium held between the first roller and the second roller while rotating around an axis. The second roller includes a shaft part, a plurality of columnar elastic members and a plurality of tube members. The shaft part extends in an axial direction and is supported rotatably around the axis. The elastic members are fixed to an outer circumferential surface of the shaft part at intervals in the axial direction. Each of the tube members has heat-shrinking property and water-repellency, adheres closely to an outer circumferential surface of the elastic member, and has both end portions which are protruded outward from both axial ends of the elastic member and have a diameter smaller than an outer diameter of the elastic member.

An image forming apparatus according to the present disclosure includes the conveyance rollers pair.

The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present disclosure is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view (front view) showing an inner structure of an image forming apparatus according to one embodiment of the present disclosure.

FIG. 2 is a sectional view (front view) showing a registration rollers pair according to the embodiment of the present disclosure.

FIG. 3 is a plan view (a partially sectional view) showing a second roller of the registration rollers pair according to the embodiment of the present disclosure.

FIG. 4 is a plan view (a partially sectional view) showing the second roller of the registration rollers pair according to a modified example of the embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereafter, with reference to the attached drawings, an embodiment of the present disclosure will be described. Note that Fr, Rr, L, R, U, and D in the drawings refer to the front, rear, left, right, upper and lower. The directional and positional terms are used herein for illustrative convenience and are not intended to limit the technical scope of the disclosure.

[Image Forming Apparatus] With reference to FIG. 1 , an image forming apparatus 1 will be described. FIG. 1 is a schematic view (front view) showing an inner structure of the image forming apparatus 1.

The image forming apparatus 1 is an inkjet printer which ejects ink droplets to form an image on a paper sheet P. The image forming apparatus 1 includes a box-shaped housing 2 in which various devices are housed. In the lower portion inside the housing 2, a sheet feeding cassette 3 in which the sheet P is set is housed, and on the upper portion of the left side surface of the housing 2, a sheet discharge tray 4 on which the printed sheet P is stacked is provided. In this specification, the direction in which the sheet P as an example of a medium is conveyed is referred to as the “conveyance direction”, and “upstream” and “downstream” and similar terms refer to the “upstream” and the “downstream” and similar concepts in the conveyance direction. The medium is not limited to the paper sheet P, but may be, for example, a sheet (film) made of resin.

In the right side portion inside the housing 2, a first conveyance path 5 is formed along which the sheet P is conveyed from the sheet feeding cassette 3 toward a head unit 12. A sheet feeding device 10 is provided at the upstream end of the first conveyance path 5, and a registration rollers pair 11 as an example of a conveyance rollers pair is provided at the downstream end of the first conveyance path 5.

The registration rollers pair 11 includes a first roller 20 and a second roller 30. The first roller 20 and the second roller 30 extend in the front-and-rear direction (the axial direction), both end portions of them are supported by a frame (not shown) provided in the housing 2 in a rotatable manner around the axes. The second roller 30 comes into contact with the first roller 20 from below, forming a nip area N (see FIG. 2 below) where the sheet P is held. The first roller 20 and the second roller 30 are connected to a drive motor (not shown) via a power transmission mechanism (not shown) such as a gear train, and are driven by the drive motor to be rotated. In the present embodiment, both the rollers 20 and 30 are driven by the drive motor to be rotated, but only one of the first roller 20 and the second roller 30 may be driven to be rotated.

The head unit 12 as an example of an image forming part has four line heads 13 corresponding to four inks of black, cyan, magenta and yellow. A plurality of recording heads 14 are mounted on each line head 13. The ink is supplied to each recording head 14 from each color ink pack (not shown) via a tube (not shown). Below the head unit 12, a conveyance belt 15 which is wound around tensioning rollers 15A is provided. A large number of through-holes (not shown) are formed in the conveyance belt 15, and a suction part 15B for sucking air through the through-holes is provided inside the conveyance belt 15.

In the left side portion inside the housing 2, a second conveyance path 6 is formed along which the sheet P is conveyed from the head unit 12 toward the sheet discharge tray 4. A decurl device 16 is provided at the midstream of the second conveyance path 6, and a sheet discharge part 17 is provided at the downstream end of the second conveyance path 6. A third conveyance path 7 is formed in the upper portion inside the housing 2, along which the sheet P is conveyed from the middle of the second conveyance path 6 to the registration rollers pair 11. A sheet conveyance rollers pair 19 which conveys the sheet P while rotating and holding the sheet P is provided at suitable positions in the first to third conveyance paths 5 to 7.

[Image Forming Processing] The image forming processing will be described. A control part (not shown) of the image forming apparatus 1 controls various controlled devices as appropriate and executes the image forming processing as follows.

The sheet feeding device 10 feeds the sheet P taken out from the sheet feeding cassette 3 to the first conveyance path 5. The leading end of the sheet P comes into contact with the first roller 20 of the registration rollers pair 11, and is guided to the nip area N. The registration rollers pair 11 temporarily blocks the sheet P, corrects the skew of the sheet P, and feeds the sheet P below the head unit 12 (on the conveyance belt 15) in accordance with the ejection timing of ink droplets from the line heads 13. The sheet P is conveyed while being attracted on the conveyance belt 15, and the head unit 12 (each recording head 14) ejects the ink droplets from the nozzles (not shown) toward the sheet P on the conveyance belt 15 to form a full-color image.

The curl of the single-sided printed sheet P is corrected by the decurl device 16, and then the sheet P is discharged to the sheet discharge tray 4 through the second conveyance path 6. When performing double-sided printing, the single-sided printed sheet P enters the third conveyance path 7, is inverted upside down and conveyed again toward the registration rollers pair 11. Then, an image is formed on the back side surface of the sheet P in the same order as in the single-sided printing described above, and the double-sided printed sheet P is discharged to the sheet discharge tray 4.

By the way, the sheet P is conventionally conveyed with its center in the front-and-rear direction (the width direction) aligned with the center of the registration rollers pair 11 in the front-and-rear direction (the axis direction). As will be described in detail later, a tube member 36 is laminated on the second roller 30 of the registration rollers pair 11 in order to suppress adhesion (transfer) of the ink on the sheet P during the double-sided printing. If a narrow sheet P is continuously conveyed, a load may be concentrated in the axial center portions of the first roller 20 and the second roller 30. Then, the center portion of the tube member 36 is shifted in the conveyance direction, and the twisted “wrinkles” are sometimes generated in the center portion of the tube member 36. When the “wrinkles” are generated in the tube member 36, the proper conveyance of the sheet P may be hindered, for example, the “wrinkles” are generated in the sheet P conveyed while being held between the registration rollers pair 11, or variation in the conveyance force of the sheet P is generated. Therefore, the registration rollers pair 11 according to the present embodiment has a structure to suppress the generation of the “wrinkles” in the surface layer (the tube member 36) of the second roller 30.

[Registration Rollers Pair] With reference to FIG. 2 and FIG. 3 , the registration rollers pair 11 will be described. FIG. 2 is a sectional view (front view) showing the registration rollers pair 11. FIG. 3 is a plan view (partially sectional view) showing the second roller 30.

As described above, the registration rollers pair 11 includes the first roller 20 and the second roller 30.

<First Roller> The first roller 20 is formed in an approximately cylindrical shape (an approximately columnar shape), made of metal such as aluminum alloy, for example, has a uniform outer diameter, and extends in the front-and-rear direction (the axial direction). Specifically, as shown in FIG. 2 , the first roller 20 is a so-called three-arrow tube in which three radially extending supports 23 are formed between a first shaft portion 21 and an outer tube 22. Both axially end portions of the first shaft portion 21 protrude outward from the outer tube 22 (the support 23), and are rotatably supported by the frame (not shown) of the housing 2.

<Second Roller> The second roller 30 is formed in an approximately cylindrical shape (an approximately columnar shape) as a whole, and conveys the sheet P held between the first roller 20 and the second roller 30 while rotating around the axis. As shown in FIG. 2 and FIG. 3 , the second roller 30 has a second shaft part 31 and two divided rollers 34. Since the two divided rollers 34 have the same shape, one divided roller 34 will be described in this specification without a case where it is specified that there are the two divided rollers.

(Second Shaft Part) As shown in FIG. 3 , the second shaft part 31 extends in the front-and-rear direction. The second shaft part 31 has a pair of rotating shaft parts 32 provided at both ends in the axial direction and a fixed shaft part 33 provided between the rotating shaft parts 32. The pair of rotating shaft parts 32 and the fixed shaft part 33 are integrally formed, and made of metal such as aluminum alloy, for example. Each rotating shaft part 32 is formed in an approximately round rod shape, and the fixed shaft part 33 is formed in an approximately cylindrical shape (an approximately cylindrical columnar shape) with a larger diameter than the rotating shaft part 32 (see also FIG. 2 ). That is, the second shaft part 31 is a so-called stepped shaft. The rotating shaft parts 32 are supported rotatably around the axes by the frame (not shown) of the housing 2. The divided rollers 34 (an elastic member 35 to be described later) are fixed to the fixed shaft part 33.

(Divided Roller) As shown in FIG. 3 , the two divided rollers 34 are arranged with a gap in the center portion in the front-and-rear direction, and are fixed to the fixed shaft part 33 of the second shaft part 31. The two divided rollers 34 is brought into contact with the lower surface of the first roller 20 (the outer tube 22) to form the nip are N (see also FIG. 2 ). As shown in FIG. 2 and FIG. 3 , the divided roller 34 has an elastic member 35 and a tube member 36.

(Elastic Member) The elastic member 35 is formed in an approximately cylindrical shape (an approximately cylindrical columnar shape), made of elastic material such as synthetic rubber, for example and has a diameter larger than that of the second shaft part 31. The two elastic members 35 are fixed to the outer circumferential surface of the second shaft part 31 (the outer pipe 22) at an interval in the front-and-rear direction (the axial direction). The elastic members 35 are provided to have the same axis as the second shaft part 31. The interval between the two elastic members 35 is set to be shorter than the axial length of each elastic member 35 (see FIG. 3 ).

(Tube Member) The tube member 36 is formed in a tube shape, and made of fluoropolymer having heat shrinking property and water-repellency, such as PFA which is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, for example. The thickness of the tube member 36 is set to be 1 to 2% (1% or more and 2% or less) of the outer diameter of the elastic member 35. The tube member 36 before a heat-shrinking treatment is formed longer in the axial direction than the elastic member 35, and has a sufficient outer diameter for the elastic member 35 to be inserted. The tube member 36 has a function of reducing friction with the sheet P and a function of preventing the ink on the sheet P passing through the nip area N of the registration rollers pair 11 from adhering to the second roller 30 during the double-sided printing. The thickness of the tube member 36 shown in the drawing is not accurate, and the tube member 36 is shown thicker for convenience of explanation.

[Manufacturing Procedure of Second Roller] Next, with reference to FIG. 2 and FIG. 3 , the manufacturing procedure of the second roller 30, specifically, the procedure of covering the elastic member 35 with the tube member 36, will be described. The following description will describe the procedure in which an operator manufactures the second roller 30 manually, but the second roller 30 may be automatically manufactured by a dedicated manufacturing device (not shown). The elastic members 35 are fixed to the second shaft part 31 (the fixed shaft part 33).

First, the operator inserts the elastic member 35 into the tube member 36, and places it inside the tube member 36. At this time, both the axial end portions 36A of the tube member 36 are made to protrude outward more than both the axial ends of the elastic member 35.

Next, the operator heats the tube member 36 using, for example, a heat gun. Then, as shown in FIG. 2 and FIG. 3 , the tube member 36 (the portion excluding both the end portions 36A) are heat-shrunk and adheres to the outer circumferential surface of the inserted elastic member 35. In addition, as shown in FIG. 3 , both the end portions 36A of the tube member 36 are also heat-shrunk to have a smaller diameter than the outer diameter of the elastic member 35. Both the end portions 36A of the tube member 36 is deformed into a tapered shape that gradually decreases in diameter toward the outside in the axial direction, covering a part of the end surface of the elastic member 35. Note that “both the end portions 36A of the tube member 36 have a smaller diameter than the outer diameter of the elastic member 35” means that at least the outermost end of the tube member 36 has a smaller diameter than the outer diameter of the elastic member 35. Also, in FIG. 3 , both the end portions 36A of the tube member 36 are in an inclined posture, and away from the end surfaces of the elastic member 35, but both the end portions 36A may be bent at an almost right angle and come into contact (close contact) with the end surfaces of the elastic member 35 (not shown).

The protrusion amount of both the end portions 36A of the tube member 36 after the heat-shrinking is determined to be 1 to 2 mm (1 mm or more and 2 mm or less) from both the axial ends (the end surfaces) of the elastic member 35. It is preferable that the length of the tube member 36 before the heat-shrinking is set such that the protrusion amount S after the heat-shrinking is 1 to 2 mm in consideration of the shrinking rate. If the protrusion amount S exceeds 2 mm, it may be cut to 1 to 2 mm. In addition, the protrusion amount S of the tube member 36 shown in the drawing is not accurate, and is longer than the proper protrusion amount S for convenience of explanation.

The second roller 30 is thus completed. The tube member 36 uses its shrinking force to be securely wound around the elastic member 35 and to envelop the entire elastic member 35.

In the registration rollers pair 11 (the conveyance rollers pair) described above, the elastic member 35 is divided into two pieces, and the tube member 36 envelops the elastic member 35. In the tube member 36, the area overlapping with the elastic member 35 adheres closely to the outer circumferential surface of the elastic member 35, and the areas protruding outward from both the ends of the elastic member 35 are tapered to cover the end surfaces of the elastic member 35. According to this configuration, even if the narrow sheet P is continuously conveyed, the load depending on the conveyance of the sheet P is distributed to the two divided rollers 34, so that the generation of twisted “wrinkles” in the tube member 36 (the surface layer of the second roller 30) can be suppressed. Thus, the proper conveyance of the sheet P by the registration rollers pair 11 can be ensured.

According to the registration rollers pair 11 according to the present embodiment, the protrusion amount S of the tube member 36 from the end surfaces of the elastic member 35 is set within a range of 1 to 2 mm and the thickness of the tube member 36 is set within a range of 1 to 2% of the outer diameter of the elastic member 35, so that the tube member 36 can be securely wound and tightened on the elastic member 35. This effectively suppresses the defects such as the generation of “wrinkles” in the tube member 36.

By the way, as shown in FIG. 3 , in the second roller 30, since the elastic member 35 is not present in the center portion in the axial direction and the second shaft part 31 (the fixed shaft part 33) is exposed, the rigidity of the entire second roller 30 is easily lowered compared with the case where the elastic member 35 is continuously fixed on the entire fixed shaft part 33. Since the second roller 30 having less rigidity is more likely to be flexed, there is a problem that the contact pressure with the first roller 20 becomes uneven. However, in the registration rollers pair 11 according to the present embodiment, the fixed shaft part 33 to which the two elastic members 35 are fixed is formed to have a larger diameter than the rotating shaft parts 32 on both the end sides in the axial direction. With this configuration, the rigidity of the fixed shaft part 33 can be improved compared with the case where the fixed shaft part 33 is formed to have the same diameter as the rotating shaft part 32. Thus, the deflection of the second roller 30 can be suppressed, the contact pressure between the first roller 20 and the second roller 30 can be made almost even, and the proper conveyance of the sheet P can be performed. The rotating shaft part 32 has a strength (rigidity) that can support the second roller 30 rotating around the axis.

[Modified Example] Incidentally, the tube member 36 in contact with the sheet P is worn by repeated conveyance. In particular, the tube member 36 is easily scraped by both the edges of the sheet P in the width direction. If a portion of the tube member 36 is scraped and thinned, the tube member 36 is easily buckled at the thinned portion and fails to properly convey the sheet P. In response to such a problem, in the second roller 40 of the registration rollers pair 11 according to the modified example of this embodiment, as shown in FIG. 4 , a plurality (for example, six) of elastic members 35 (the divided rollers 34) are arranged at positions avoiding both the edges in the width direction of the sheets P. As a specific example, the six elastic members 35 are arranged so as not to touch both the edges of various sizes of sheet P, such as A4 size and B5 size. That is, both the edges of the sheet P correspond to the gaps between adjacent elastic members 35. With this configuration, since both the edges of the sheets P do not come into contact with the tube member 36, which is the surface layer of the elastic member 35, the wear of the tube member 36 by both the edges of the sheet P can be suppressed. As a result, a portion of the tube member 36 is prevented from being scraped and thinned, and the sheet P can be properly conveyed over a long period of time.

In the registration rollers pair 11 according to the present embodiment (including the modified example, the same shall apply hereafter), the second rollers 30 and 40 have the two or six elastic members 35 (the divided rollers 34), but the present disclosure is not limited to this. As long as two or more elastic members 35 are fixed to the second shaft part 31, the number can be changed freely.

In the registration rollers pair 11 according to the present embodiment, the fixed shaft part 33 of the second shaft part 31 is formed thicker than the rotating shaft parts 32, but the present disclosure is not limited to this. Although the effect of improving the rigidity of the fixed shaft part 33 is eliminated, the fixed shaft part 33 may be formed to have the same diameter as the rotating shaft part 32 (not shown).

In the registration rollers pair 11 according to the present embodiment, the protrusion amount S of both the end portions 36A of the tube member 36 is 1 to 2 mm, and the thickness of the tube member 36 is 1 to 2% of the outer diameter of the elastic member 35, but the present disclosure is not limited to this. The protrusion amount S and the thickness of both the end portions 36A of the tube member 36 may be changed as appropriate to the extent that the generation of “wrinkles” in the tube member 36 is suppressed and the proper conveyance of the sheet P can be ensured.

In the present embodiment, the features of the present disclosure are applied to the registration rollers pair 11 as an example of a conveyance rollers pair, but it is not limited to this, and may be applied to the sheet conveyance rollers pair 18, for example (not shown).

In the image forming apparatus 1 described above, the recording head 14 ejects the ink droplets from the nozzles, but the droplets ejected from the nozzles are not limited to the ink droplets, and may be water, liquid adhesive or liquid synthetic resin, for example.

The image forming apparatus 1 described above is a color printer, but it is not limited to this, and may be a monochrome printer, a copying machine, a facsimile machine or the like. In addition, the image forming method of the image forming apparatus 1 is not limited to the inkjet type, but may be an electrophotographic type.

The description of the above embodiment shows one aspect of the conveyance rollers pair and the image forming apparatus according to the present disclosure, and the technical scope of the present disclosure is not limited to the above embodiment. The disclosure may be variously modified, replaced, or modified to the extent that it does not deviate from the purport of the technical idea, and the scope of the patent claims includes all of the implementations that may be included within the technical idea. 

1. A conveyance rollers pair comprising: a first roller extending in an axial direction, having a uniform outer diameter and rotating around an axis; and a second roller conveying a medium held between the first roller and the second roller while rotating around an axis, wherein the second roller includes: a shaft part extending in an axial direction and supported rotatably around the axis; and a plurality of columnar elastic members fixed to an outer circumferential surface of the shaft part at intervals in the axial direction; and a plurality of tube members each having heat-shrinking property and water-repellency, adhering closely to an outer circumferential surface of the elastic member, and having both end portions which are protruded outward from both axial ends of the elastic member and have a diameter smaller than an outer diameter of the elastic member.
 2. The conveyance rollers pair according to claim 1, wherein the elastic members are arranged in positions that avoid both ends of the medium in a width direction parallel to the axial direction.
 3. The conveyance rollers pair according to claim 1, wherein the shaft part includes: rotating shaft parts provided at both ends in the axial direction and supported rotatably; and a fixed shaft part formed between the rotating shaft parts, having a larger diameter than the rotating shaft parts and to which the elastic members are fixed.
 4. The conveyance rollers pair according to claim 1, wherein an amount of protrusion of the end portions of the tube member is 1 to 2 mm, and a thickness of the tube member is 1 to 2% of the outer diameter of the elastic member.
 5. The conveyance rollers pair according to claim 1, wherein the end portions are heat-shrunk to have an outer diameter smaller than an outer diameter of the elastic member.
 6. An image forming apparatus comprising the conveyance rollers pair according to claim
 1. 7. The image forming apparatus according to claim 5, wherein the first roller is made of metal, and the conveyance rollers pair is a registration rollers pair that blocks the medium temporarily and then feeds the medium toward an image forming part that forms an image on the medium.
 8. The image forming apparatus according to claim 7, wherein the medium comes into contact with the first roller and then is temporarily blocked. 